For example, in a hydrometallurgical method for nickel oxide ore, a sulfurization treatment is performed in such a manner that hydrogen sulfide gas is blown into a solution obtained by neutralizing a leach solution of nickel oxide ore or a solution for nickel recovery from which impurities are removed, whereby a metal sulfide is formed.
The hydrogen sulfide gas to be used at this treatment is manufactured, for example, by a plant for manufacturing hydrogen sulfide gas configured to manufacture hydrogen sulfide. The plant for manufacturing hydrogen sulfide gas includes a facility configured to manufacture hydrogen sulfide gas, a facility configured to cool generated hydrogen sulfide gas, a facility configured to recover sulfur contained in the hydrogen sulfide gas, and the like. Such plants for manufacturing hydrogen sulfide are mainly classified into two, namely, plants which use a catalyst as illustrated in FIG. 3 and plants which use no catalyst as illustrated in FIG. 4.
Specifically, a plant for manufacturing hydrogen sulfide gas 50 illustrated in FIG. 3 includes: a reaction facility 51 configured to generate hydrogen sulfide gas from supplied sulfur and supplied hydrogen gas; a cooling facility 52 configured to cool the hydrogen sulfide gas; a washing facility 53 configured to wash sulfur contained in the hydrogen sulfide gas; and a drying facility 54 configured to dry hydrogen sulfide gas after the washing to remove moisture therefrom. Furthermore, the plant for manufacturing hydrogen sulfide gas 50 includes incidental facilities, namely, a storage facility 55 configured to store produced hydrogen sulfide gas and a supply facility 56 configured to supply the hydrogen sulfide gas.
In the plant for manufacturing hydrogen sulfide gas 50, a catalyst is used inside a reactor of the reaction facility 51 in order to reduce activation energy. Furthermore, in the plant for manufacturing hydrogen sulfide gas 50, sulfur contained in manufactured hydrogen sulfide gas is removed by the washing facility 53, and then, moisture is removed by the drying facility 54, whereby the corrosion of facilities due to moisture is prevented.
Furthermore, in the plant for manufacturing hydrogen sulfide gas 50, using the supply facility 56 such as a compressor, the pressure of manufactured hydrogen sulfide gas is increased to a required pressure, and the hydrogen sulfide gas having the increased pressure is supplied to, for example, a plant which uses hydrogen sulfide gas in a dezincification step, a sulfurization step, or the like in the foregoing hydrometallurgical method of nickel oxide ore.
In the plant for manufacturing hydrogen sulfide gas 50, as conditions for manufacturing hydrogen sulfide gas, for example, at a pressure of approximately 5 kPaG and a temperature of approximately 380° C., operations are carried out. In this plant for manufacturing hydrogen sulfide gas 50, a catalyst is used for the reaction facility 51, and therefore, operations can be carried out under low pressures and low temperatures, and this point constitutes an operational advantage.
However, in the plant for manufacturing hydrogen sulfide gas 50, it is necessary to periodically replace a catalyst in the reaction facility 51, and besides, from a viewpoint of the life of a catalyst, it is necessary to strictly control the quality of sulfur, that is, a raw material of hydrogen sulfide gas.
On the other hand, a plant for manufacturing hydrogen sulfide gas 60 illustrated in FIG. 4 is a plant which does not use a catalyst in a reactor. As illustrated in FIG. 4, the plant for manufacturing hydrogen sulfide gas 60 includes: a reaction facility 61 (a reactor 66, a quench tower 67, a heater 68) configured to generate hydrogen sulfide gas from sulfur and hydrogen gas; cooling facilities 62 (62A, 62B) configured to cool the hydrogen sulfide gas; a knockout facility 63 configured to remove sulfur contained in the hydrogen sulfide gas and supply the hydrogen sulfide gas; and a blowdown facility 64 configured to recover the sulfur removed from the hydrogen sulfide gas and supply the sulfur to a sulfur treatment plant or the like. Furthermore, the plant for manufacturing hydrogen sulfide gas 60 includes a facility 65, as an incidental facility, configured to cool the temperature of sulfur to adjust a heat balance.
In the plant for manufacturing hydrogen sulfide gas 60, molten sulfur is stored in the reactor 66 of the reaction facility 61, and hydrogen gas is supplied from the lower portion of the reactor 66, whereby, during hydrogen gas passes the molten sulfur, a formation reaction of hydrogen sulfide gas proceeds. It should be noted that sulfur, which is decreased by the reaction, is supplied from the upper portion of the reaction facility 61. Most of the hydrogen sulfide gas formed in the reaction facility 61 is hydrogen sulfide, but, the hydrogen sulfide gas contains sulfur steam which is caught when hydrogen gas passes through the inside of the reactor.
Furthermore, in the plant for manufacturing hydrogen sulfide gas 60, as conditions for manufacturing hydrogen sulfide gas, for example, under high pressure and temperature, that is, at a pressure of approximately 800 kPaG and a temperature of approximately 470° C., operations are carried out. The temperature of formed hydrogen sulfide gas decreases to approximately 150° C. at the time when the gas leaves the quench tower 67 constituting the reaction facility 61, and furthermore, the gas is cooled to approximately 50° C. (a temperature used in a supply destination facility) by the cooling facility 62, and transported to the knockout facility 63.
Furthermore, a great operational-trouble is caused when most of sulfur contained in hydrogen sulfide gas generated in the reaction facility 61 adheres to valves, such as a control valve and a manual valve, and meters, such as a thermometer and a pressure gauge, in a plant or the like which is a supply destination and uses hydrogen sulfide gas. Therefore, the gas is solidified once by the knockout facility 63, and sulfur deposited on the bottom of the knockout facility 63 is heated by steam via a jacket provided in the lower perimeter of the knockout facility 63, thereby being melted and recovered. The recovered sulfur is stored in the blowdown facility 64, and then, using a supply pump 69, the sulfur is supplied to a sulfur treatment plant to be processed or repeatedly used.
In this manner, sulfur contained in hydrogen sulfide gas generated in the plant for manufacturing hydrogen sulfide gas 60 is separated from the hydrogen sulfide gas by a knockout drum, and then, the hydrogen sulfide gas is supplied to, for example, a plant which uses hydrogen sulfide gas in a dezincification step, a sulfurization step, or the like in the foregoing hydrometallurgical method of nickel oxide ore.
In the plant for manufacturing hydrogen sulfide gas 60, operations are controlled in a state in which a pressure in a system is maintained high, and therefore, facilities, such as a compressor and a chiller, are unnecessary, whereby an initial investment can be reduced. Furthermore, the plant for manufacturing hydrogen sulfide gas 60 has an advantage that periodic catalyst replacement like the foregoing one performed in the plant for manufacturing hydrogen sulfide gas 50, costs for this replacement, and maintenance costs including the quality control of sulfur are not required, whereby operation costs can be reduced.
However, in the plant for manufacturing hydrogen sulfide gas 60, operations are performed under high pressure and temperature, and therefore, the danger associated with gas leakage is increased.
Since hydrogen sulfide gas is a very hazardous substance, it is necessary to take measures against gas leakage, and for example, it is necessary to enclose a hydrogen sulfide gas manufacturing facility by a building, a shelter, or the like, or to take the direction of wind into consideration.
Hydrogen sulfide gas is usually treated by a detoxifying tower, a scrubber, or a flare facility. In the case of a treatment using a flare facility, hydrogen sulfide gas is burned to generate SOx, and consequently, an environmental problem arises. On the other hand, in the case of a treatment using a detoxifying tower or a scrubber, an environmental problem does not arise, but, a neutralizer such as caustic soda is needed to neutralize hydrogen sulfide gas, and accordingly the cost of a neutralizer is required. A detoxifying facility, a scrubber, and a flare facility are operated even when hydrogen sulfide gas does not leak. Hence, in the case of a detoxifying facility and a scrubber, a neutralizer is additionally required for that operation, thereby leading to higher costs.
In the plant for manufacturing hydrogen sulfide gas 60, it has been desired that, while safety in exhausting hydrogen sulfide gas is maintained, the amount of a neutralizer used is reduced to achieve cost reduction.